On-chip microresonator frequency combs: Generation dynamics, power transfer, and time-domain characterization
Over the last two decades, optical frequency combs from a mode-locked laser have been used as a ruler in frequency domain for extremely precise measurements. With a series of peaks equally spaced in optical frequency, it gives a significant improvement on the increasing demands of optical frequency metrology, telecommunication, optical clocks and measurements on the atomic level. However, optical frequency combs, based on fiber or free-space optics, are now restricted by further downsizing the optical paths and therefore, with these conventional combs, it is hard to achieve a repetition rate in radio frequencies ranging from several tens GHz to THz. Recently, high-quality (Q) microresonators offer the potential for on-chip comb generation with a repetition rate from tens GHz to several THz. These frequency combs may also support the generation of octave-spanning comb spectra in compact and chip-level devices. This novel Kerr comb technology benefits the developments of integrated photonics. Here, in this thesis, the author discusses the microresonator-based frequency combs from silicon nitride waveguide microrings. Owing to its compatibility with CMOS-compatible fabrication process and large Kerr nonlinearity, silicon nitride has attracted considerable attention for on-chip comb generation. The thesis is organized as follows: Chapter 1 gives brief reviews of optical frequency combs and the properties of silicon nitride waveguide resonators. In Chapter 2, on-chip comb generation and the properties of the generated combs, including communication performance, intensity noise, and time-domain characterization, are investigated. A drop-port study and power transfer in microrings are presented in Chapter 3. The comb-enhanced coupling, comb threshold, and comb efficiency at the through port are also discussed. In Chapter 4, the author compares the comb generation in both normal and anomalous cavity dispersion. Time-domain autocorrelation measurements will be demonstrated to characterize the comb generation in different dispersion regimes. In Chapter 5, the mode-locking transition and soliton formation in anomalous dispersion regime will be discussed. A short, bright, and close to transform-limited pulse is identified in time with a drop-port geometry. Finally, a summary is given in Chapter 6.
Weiner, Purdue University.
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